Immunologic tests of value in diagnosis. 2. Complement.

Laboratory tests are available to assess the function of the complement pathway and to measure levels of individual complement components. The pattern of complement abnormalities is often helpful in suggesting diagnostic possibilities. For example, when when total hemolytic complement, C3, and C4 are all decreased, one of the rheumatoid diseases is likely.

Immunologic tests of value in diagnosis. 1. Acute phase reactants and autoantibodies.

Acute phase reactants are nonspecific indicators of tissue necrosis and/or inflammation but may be helpful in determining activity of disease. Rheumatoid factor is likewise rather nonspecific, but its presence is helpful in predicting the course, severity, and complications of rheumatoid arthritis. Numerous antinuclear antibodies have been identified in collagen vascular diseases; perhaps the most specific association is between anti-Sm antibody and systemic lupus erythematosus.